The present invention relates to a spectrum measuring apparatus that measures spectrum intensity of wide wavelength of a vacuum ultraviolet region to an infrared region that irradiated from an EUV light source.
Conventionally, in photolithography process to manufacture fine semiconductor devices such as semiconductor memory and logic circuit, a reduction projection exposure that uses ultraviolet light is done. The minimum critical dimension transferred by the projection exposure is proportional to the wavelength of light used for transfer and inversely proportional to the numerical aperture (“NA”) of the projection optical system. Therefore, to transfer the fine circuit pattern, shorter ultraviolet light wavelengths have been proposed—from an ultra-high pressure mercury lamp (i-line with a wavelength of approximately 365 nm) to KrF excimer laser (with a wavelength of approximately 248 nm) and ArF excimer laser (with a wavelength of approximately 193 nm).
However, lithography using ultraviolet light has limitations when it comes to satisfying the rapidly promoted fine processing of a semiconductor device. Therefore, a reduction projection optical system using extreme ultraviolet (“EUV”) light with a wavelength of 10 to 15 nm shorter than that of the ultraviolet has been developed to efficiently transfer very fine circuit patterns of 100 nm or less. FIG. 11 is a conceptual rendering of the exposure apparatus that uses the EUV light.
The EUV light source uses, for example, a light source of laser plasma (LPP) method or a light source of discharge plasma (DPP) method.
The EUV light source of LPP method irradiates a highly intensified pulse laser beam to a target material put in vacuum, thus generating high-temperature plasma for use as EUV light with a wavelength of about 13 nm emitted from this. The target material may use a metallic thin film, inert gas, and droplets, etc., and is supplied by a means such as a gas jet in the vacuum. The pulse laser preferably has high repetitive frequency, e.g., usually several kHz, for increased average intensity of the emitted EUV light from the target.
On the other hand, the EUV light source of DPP method flows a gas such as Xenon between electrodes, generates the plasma with the electrical discharge, and generates the EUV light.
When the EUV light used for the exposure, the EUV light is absorbed by using a usual metallic mirror and a lens made of quartz etc. A multilayer mirror that laminates 20 layers with a molybdenum (Mo) layer and a silicon (Si) layer is used for the EUV light. In general, the multilayer mirror is adjusted by changing the thickness of the each layer of the multilayer so that reflectivity to the EUV light with a wavelength of 13.5 nm is high, and the EUV light with other wavelengths are absorbed by the mirror.
An optical system for the EUV exposure apparatus is composed with several multilayer mirrors. Especially, the EUV light source of LPP method arranges a condenser mirror surrounding the emission point to efficiently use the EUV light emitted from the target, and to condense the generated EUV light to a predetermined light wavelength.
The light emitted from the target includes not only the EUV light with the specific wavelength used for the exposure from the EUV light source of laser plasma method but also the light with a wavelength band such as the EUV light, X-ray, ultraviolet light, visible light and infrared light. Thereby, the EUV light with a wavelength different than the specific wavelength and X-ray light that can not be reflected by the multilayer mirror are absorbed by the multilayer mirror, and causes the rise in heat of the mirror. Moreover, the ultraviolet light activates a residual gas in the vacuum, and accelerates a deposition of a contamination on the condenser mirror. The light of the ultraviolet region to the infrared region is reflected by the multilayer mirror that composes the optical system of the exposure apparatus, and reaches a wafer. The light of the ultraviolet region to the infrared region is absorbed by resist, and heat expands the wafer. As the result, there is a possibility of decreasing overlay accuracy during exposure.
Therefore, it is necessary to measure the wide band spectrum of the light emitted from the EUV light source, and to measure the light intensity of the light discharged in each wavelength region precisely, to design the exposure apparatus that uses the EUV light and exposure.
An apparatus that is described to FIG. 12 is disclosed in Japanese Laid-Open Patent Application No. 2002-175980 (correspond with U.S. Patent Publication No. 2002/085286) about the measurement of the EUV light emitted from the EUV light source. In FIG. 12, the EUV light emitted from a condenser point 101 decreases the intensity of the light by an aperture stop 105, and reflects with a multilayer mirror 102. Moreover, the EUV light reaches a CCD array 104 through an EUV filter 103 that transmits only an EUV light of a target for the measurement and is measured.
Details of spectrum of the EUV light of a predetermined wavelength region can be measured by a grazing incidence spectrum system shown in FIG. 13. This method uses the multilayer mirror as the filter, e.g., two multilayer mirrors 201 and 202. The system can measure the wavelength region of about 5 to 50 nm, and can measure detail spectrum shape because it adjusts a wavelength resolution (λ/Δλ) to 500 or more.
However, the above-mentioned measuring apparatuses comparatively measure only a part of the light emitted from the EUV light source for the wavelength region in the narrow range. Thereby, it is difficult to measure the entire wide band spectrum of the light emitted from the EUV light source, and to know the absolute intensity. As the result, the wavelength intensity distribution of entire beams including the infrared ray region emitted from the EUV light source necessary to design the exposure apparatus that uses the EUV light and exposure stability can not be obtained.